When populating multilayer circuit boards with electronic components, it is known to solder components without connecting leads, e.g. so-called LCCC (leadless ceramic chip carrier) components, directly onto corresponding connecting surfaces of the multilayer circuit board. When thermal shock loads occur, the different coefficients of thermal expansion of the ceramic chip carriers and the circuit board result in shear forces which must be absorbed by the soldered connections of the component. With severe temperature fluctuations, such as occur in particular in space technology, for example in a satellite orbiting the earth, the difference in thermal expansion between large-area ceramic components and the circuit board would lead to damage to the soldered connections and failure of the assembly. In the case of a satellite located in space, a soldered connection defect of this kind is extremely disastrous, since it generally leads to failure of the unit in question. To solve this problem, it is known to use multilayer circuit boards having a core substrate. Core substrates made of metal or composite carbon fiber materials are known.
U.S. Pat. No. 4,921,054, for example, discloses a thermomechanically adapted multilayer circuit board having two core substrates, made of copper-plated Invar, which control the expansion behavior of the circuit board. The layered composite material made up of the core substrates and circuit board material is produced by stacking and pressing. The coefficient of expansion of the overall arrangement comprising insulating material, conductor path layers, and core substrates are determined by the proportion of the total thickness of the layered composite accounted for by the core substrate. Since the core substrate has a much lower coefficient of thermal expansion than the circuit board material, which as a rule is made of an epoxy/glass material, it is possible for the resulting coefficient of thermal expansion of the multilayer circuit board equipped with the core to be adapted to the coefficients of expansion of the ceramic components. Disadvantageous shear forces which might damage the soldered connection therefore do not occur in the coverage area of the components.
Despite the advantages of the known multilayer circuit boards, producing the through-plated holes guided through the core substrate is extremely complex. A further disadvantage is that the core substrates extending over the entire surface extent of the circuit board greatly increase the weight of the circuit board, which is extremely undesirable in space technology. It is also disadvantageous that the known core substrates increase the size of the multilayer circuit board. Since conductor paths cannot be laid out in the plane of the core substrate, either the thickness of the circuit board must be increased or the circuit board must be enlarged laterally. Both are extremely undesirable, since the space available, especially in space technology, is extremely limited.